In recent years, certain high performance bicycles have included hydraulic disc brakes. Hydraulic disc brake systems typically include a caliper housing, a first movable brake pad and a second fixed or movable brake pad. The movable brake pad is typically attached to a piston that is movable in response to fluid pressure applied via a hydraulic fluid conduit in the caliper housing. The brake pads are positioned on either side of a rotor, which is attached to the front or back wheel of a bicycle. Upon the application of fluid pressure to the piston or pistons, the brake pads come into contact with the rotor, thereby applying frictional resistance and causing the bicycle to slow down or stop.
Hydraulic disc brake systems for bicycles are typically actuated by a brake lever attached to a bicycle handlebar. They also typically include a master piston in a master cylinder which is actuated by the brake lever. The master cylinder contains a hydraulic fluid and is in fluid communication with the disc brake caliper via a fluid conduit. The brake pads are typically spaced apart from the rotor by a predetermined gap. As the lever is contracted towards the handlebar, the master piston moves, thereby forcing liquid out of the master cylinder and into a conduit connected to the caliper housing. The movement of fluid into the caliper housing causes the pistons to move, eventually bringing the brake pads into contact with the rotor.
When initially filling the hydraulic disc brake system (including the master cylinder and the caliper), the system must be bled to remove gas bubbles from the system and optimize performance of the brakes. Some prior art calipers include what is called a banjo fitting that includes a banjo bolt. A banjo fitting comprises a perforated hollow bolt and spherical union for fluid transfer. The name stems from the shape of the fitting, having a large circular section connected to a thinner pipe, generally similar to the shape of a banjo. However, during bleeding, bubbles are often caught inside the hollow axial portion of the typical banjo bolt. A need exists for a bolt used with a hydraulic disc brake that is easy to bleed.